DE 195 16 97 describes a drive unit having an internal combustion engine having turbocompound design. In this unit, a turbine is provided to which exhaust gas is fed from the internal combustion engine during the traction mode in order to drive the turbine. The turbine has a drive connection to the crankshaft via a hydrodynamic clutch. In this way it is possible to utilize the residual energy still present in the exhaust gas.
In the aforesaid drive unit, a further exhaust line is connected downstream of the turbine. An exhaust valve is provided in this exhaust line. At the changeover from the traction mode to the braking mode, the exhaust valve is closed. As a result, an exhaust gas pressure which causes the exhaust valve to open when a certain value is reached builds up behind the turbine.
DE 37 28 681 C2 and DE 39 04 399 A1 also describe drive units with devices for recovering exhaust gas energy.
Drive units of this type have the advantage that the residual heat which is contained in the exhaust gas is utilized—if appropriate after the exhaust gas has passed through an exhaust gas turbocharger. However, said drive units do not contribute directly to the braking in braking mode. The aforesaid exhaust valve performs the customary exhaust gas braking throttling which is known per se.
The invention is based on the object of configuring a drive unit of the aforesaid type in such a way that not only the residual energy contained in the exhaust gas is utilized in the traction mode but also in such a way that the drive unit contributes to the braking in the braking mode.